Frequency spectrum available for wireless communications is limited and must be intelligently used. Intelligent frequency spectrum usage can include improving the efficiency of frequency spectrum utilization. By intelligently sharing frequency spectrum, wireless devices can co-exist with each other, and obtain higher overall utilization of the frequency spectrum than if the wireless devices were to co-exist by, for example, limiting the power levels of transmission signals to minimize interference of each wireless device with the other.
One example of intelligent frequency usage includes detect and avoid (DAA). DAA devices “listen” for other signals while transmitting in a given frequency spectrum at a predetermined emission level. If a DAA device senses another wireless device operating in the same frequency range, the device either lowers its output power, or switches to another frequency. By doing this, the device can avoid interfering with the other device, and at the same time, not have to satisfy burdensome transmission restrictions when the other device is not present.
FIG. 1 shows a typical communication link between a first transceiver 110 and a second transceiver 130. The transceivers 110, 130 can include transmission signals that interfere with a victim transceiver 140 of, for example, another network. As shown, the intended communication link of the victim transceiver 140 includes communication signals having a transmission frequency of fm. A network (such as the transceivers 110, 130) employing DAA senses the transmission frequency fm of the victim transceiver 140 and attempts to avoid the transmission frequency fm, thereby minimizing interference with the victim transceiver.
Effective implementations of DAA provide efficient avoidance. That is, the wireless device avoids only the portion of the frequency spectrum that might cause interference with another wireless device (victim receiver). If a wireless device transmits a signal having a wide bandwidth, the wireless device may be required to avoid a small portion of frequency spectrum being used by a victim receiver. A digital baseband processor of the wireless device can be controlled to modify the signal modulation to create a new waveform in which the portion of the frequency spectrum to be avoided is notched out. In practice, however, this is not so easy. Generally, distortion caused by analog circuits within analog circuit portions of the wireless device cause spectral leakage to fill in the notch created by the digital baseband processor.
It is desirable have a method and apparatus for reducing spectral leakage of wireless devices, thereby improving performance of DAA systems. The method and apparatus should be capable of reducing spectral leakage due to both frequency-dependent and frequency-independent I-Q imbalance in the wireless devices. Desirably, the method and apparatus do not require specialized or additional electronic circuitry.